I have dual nationality (Swiss and USA). I have contributed to the Swiss pension fund every year since 1980 and to the US pension since 1999. Can I claim both pensions when I retire?
Possibly, but if you draw receive a Swiss pension and US Social Security retirement benefits, your US Social Security benefit rate will likely be reduced due to the Windfall Elimination Provision, or WEP (https://www.ssa.gov/pubs/EN-05-10045.pdf). The maximization software available on this website is programmed to handle benefit computations involving WEP, so you may want to use it in order to explore your options.
For more information, refer to the Social Security website: https://www.ssa.gov/international/Agreement_Pamphlets/switzrld.html.